The IEEE 802.11 active probing analysis and enhancements

The active probing mechanism is a critical function of the IEEE 802.11 protocol. Active probing is used for access points discovery, roaming between different access points, and recently in WLAN-based location determination systems to achieve reliable signal strength measurements. The 802.11 standard leaves it open for manufacturers to implement the active probing mechanism. In this paper, we analyze the performance of the active probing mechanism of the 802.11 protocol. Our analysis shows that the current implementations of the active probing mechanism are inefficient and lead to decreased capacity. We identify two main factors contributing to this negative effect on the capacity. These factors are observed with cards from different manufacturers and lead to increasing the probing cycle time and unnecessary retransmission. We propose different techniques to enhance the efficiency of the active probing mechanism. The proposed techniques require no or minimal changes to the wireless cards´ drivers and hence allow incremental deployment.